Asteroid from Another Star System Found Orbiting Our Solar System for the First Time

May 21, 2018

Images of asteroid 2015 BZ509, which appears to have come from another star system.Photograph: Royal Astronomical Society

A permanent visitor from interstellar space has been found in our solar system, astronomers studying an asteroid orbiting our sun have revealed.

While collisions with Earth by comets and asteroids from within our solar system are thought to have brought organic material and water necessary for life to emerge, experts say the latest discovery suggests bodies from beyond the solar system might have also have played a role.

“It would be very interesting to go and observe it more and understand its composition,” said lead author Dr Fathi Namouni from the Observatoire de la Côte d’Azur.

“Before [the discovery of this asteroid], we only had to work to explain solar system phenomena with the objects that are in the solar system and thought to be part of the solar system all the time,” he said. “Now we have new sources of material that actually influenced the solar system – and so the solar system did not grow up in isolation.”

The latest discovery marks the first time an asteroid that appears to be a permanent member of our solar system has been revealed as having its origins in another star system. ‘Oumuamua, an asteroid spotted hurtling through our solar system earlier this year, was only on a fleeting visit.

Known as asteroid 2015 BZ509, the permanent visitor is about 3km across and was first spotted in late 2014 by the Pan-Starrs project at the Haleakala Observatory in Hawaii. Experts quickly realised the asteroid travelled around the sun in the opposite direction to the planets – a retrograde orbit.

Further work on the asteroid revealed it takes the same length of time to orbit the sun as the planet Jupiter at a similar average distance, although in the opposite direction and with a different shaped path, suggesting the two have gravitational interactions.

But unpacking quite where the asteroid came from was challenging.

Asteroids that orbit the sun on paths that take them between the giant planets – Jupiter, Saturn, Uranus and Neptune – are known as centaurs, and it is thought that many might come from distant bands of material within the solar system such as the scattered disk or the Oort cloud. Several, like BZ509, are known to have retrograde paths, although how they ended up on such orbits is unclear.